1. Field of the Invention
The present invention relates to an electronic apparatus in which connectors are mounted on both ends of a printed circuit board, respectively. In particular, the present invention relates to an electronic apparatus with a structure that reduces an influence of electrostatic discharge in transmitting or receiving a signal with respect to external equipment connected to each of the connectors.
2. Description of the Related Art
An image forming apparatus that is an example of the electronic apparatus generally includes an operating device configured to be operated by a user. The operating device of this type includes a printed circuit board housed in a case, and a conductive chassis plate disposed below the printed circuit board, in which the printed circuit board is grounded to the conductive chassis plate (see Japanese Patent Application Laid-Open No. 2006-100711). When static electricity charged on a human body is discharged to the operating device, the static electricity that has entered the printed circuit board is allowed to escape to the conductive chassis plate. In the grounded structure, portions of the conductive chassis plate corresponding to corners (four corners) at both ends of the printed circuit board are bent upward to form projecting portions, and the projecting portions are electrically connected to ground wiring patterns at the corners of the printed circuit board with conductive screws or the like. With the grounded structure, the printed circuit board is supported to the conductive chassis plate.
Further, in order to upsize the operating device supporting multiple functions and improve the operability, there has been known an operating device provided separately from an apparatus main body of the image forming apparatus. A bar-shaped conductive support member is projected from the apparatus main body, and the support member is connected to a vicinity of a central portion of a lower surface of the conductive chassis plate to support the operating device. A length of one side of the conductive chassis plate needs to be set to be equal to or larger than a length of the printed circuit board so that the printed circuit board is grounded. However, from the viewpoint of saving the space, the length of one side of the conductive chassis plate is generally set to be equal to the length of the printed circuit board.
In recent years, because needs to transfer data directly with respect to external equipment such as a memory media and not through a computer terminal are increased, there has been proposed a structure in which connectors for connecting the external equipment to both ends of the printed circuit board are provided. For example, a connector into which a memory media such as a card type memory is detachably inserted is mounted on one end of the printed circuit board, and a connector into which a memory media such as a USB memory is detachably inserted is mounted on the other end of the printed circuit board. Each signal terminal of those connectors is connected to an IC mounted on the printed circuit board by a wiring pattern. Those connectors for the memory media enable data within the memory media to be read directly and not through the computer terminal, to thereby form an image on a sheet. Further, those connectors enable an image to be read from an image reading device of the image forming apparatus, and enable data to be saved directly in the memory media and not through the computer terminal.
On the above-mentioned printed circuit board, a portion at which static electricity is liable to be discharged from the external is covered with an insulator to block the entrance of static electricity. Further, because the connector to and from which the external equipment is attachable and detachable from the external of a casing is mounted on each end of the printed circuit board, there is a fear in that static electricity is discharged from each connector. For that reason, each connector is configured to allow static electricity to flow in the ground wiring pattern of the printed circuit board so that static electricity is prevented from directly entering the IC from the connector.
However, even if static electricity is allowed to flow into the ground wiring pattern of the printed circuit board in the connector mounted on the other end of the printed circuit board, the connector mounted on one end of the printed circuit board may be affected by electrostatic discharge. Specifically, when the user executes the attachment/detachment work of the external equipment with respect to the connector mounted on the other end of the printed circuit board, static electricity is applied to the connector. An electrostatic discharge pulse that has been applied to the connector mounted on the other end of the printed circuit board flows toward one end of the printed circuit board through the ground wiring pattern of the printed circuit board, and flows into the conductive chassis plate from one end of the printed circuit board. In this case, one end of the conductive chassis plate functions as an open end with respect to the applied electrostatic discharge pulse, and a large voltage fluctuation occurs. Further, because one end of the conductive chassis plate and one end of the printed circuit board are aligned and electrically connected to each other at the projecting portion, those ends come close to each other. Likewise, a large voltage fluctuation occurs at one end of the printed circuit board. When the external equipment is connected to the connector mounted on one end of the printed circuit board, there is a fear in that the voltage fluctuation affects the transmission or reception of the signal with respect to the external equipment.
To cope with this problem, a method of inserting a static electricity countermeasure component such as a diode or a varister into a signal wire that is liable to be affected by static electricity has been proposed. However, this method suffers from problems such as an increase in the component costs and a reduction in the package density on the printed circuit board. Therefore, another countermeasure has been desired.